NIAAA has designated underage drinking as a priority research area. Of note, the highest prevalence of problem alcohol use is among young adults ages 18-25. Heavy drinking that occurs during this period can have important immediate and lifelong adverse consequences. Behavioral interventions, notably BASICS (Brief Alcohol Screening and Intervention for College Students), have been developed to help young adults reduce their drinking. Although these interventions are effective, including with college students mandated to treatment and others with minimal motivation to stop drinking, the effect sizes are modest, suggesting that new approaches are needed to enhance these interventions. A promising strategy yet to be tested in young adults is the use of the opiate antagonist naltrexone. In other research, naltrexone has been shown to reduce the amount of alcohol consumed, even in the absence of strong internal motivation to change, and to reduce the frequency of any and heavy drinking in problem drinkers seeking treatment. Thus we propose to conduct an 8 week double-blind placebo-controlled trial to test the combined efficacy of BASICS + naltrexone in 132 young adults aged 18-25 who drink heavily. A novel strategy will be used for administering low-dose naltrexone, in which daily dosing will be combined with targeted dosing in anticipation of high-risk situations. The main hypotheses are that daily + targeted naltrexone will result in greater reductions in frequency of heavy and any drinking compared with daily + targeted placebo. In order to enhance the sensitivity with which we are able to assess naltrexone's effects on drinking, daily ratings will be obtained during treatment. These will permit us to examine alternative measures of alcohol involvement (e.g., reports of subjective intoxication, estimated blood alcohol levels) in addition to the traditional measures based on number of drinks consumed. These data will also be used to examine potential mediators (e.g., craving, subjective effects of alcohol) of treatment response in order to better understand the effects of naltrexone. The durability of treatment effects will be examined at 3, 6 and 12 months after randomization. Demonstration of the efficacy of naltrexone in this population will provide the essential information needed for its adoption by college counseling centers and other health care settings committed to reducing the risk of heavy drinking in young adults.